The present invention relates to a drill bit having an exchangeable cutting portion.
The term “drill bit” should be understood to encompass all drilling tools having a hollow, cylindrical drill shaft having one or more cutting elements, for example, core drill bits and drill bits for socket outlets. Independently of their intended use, the drill bits may comprise additional elements such as, for example, a depth stop that limits the depth of the bore.
Drill bits are comprised of a cutting portion having one or more cutting elements, a drill shaft portion, and a receiving portion having an insertion end. The drill bit is attached in the tool receptacle of a core drill via the insertion end and, during drilling operation, driven by the core drill in a rotational direction around an axis of rotation. Known drill bits are divided into drill bits having an exchangeable cutting portion and drill bits without an exchangeable cutting portion, with the drill bits having an exchangeable cutting portion being further divided into detachable and non-detachable connections. A connection is considered detachable if the connection can be detached by the user in a non-destructive manner such as, for example, a plug-and-socket connection, a screw connection, or a magnetic connection. A connection is considered non-detachable if the user is able to release the connection only by destroying the fastener such as, for example, a solder connection, a welded connection, a riveted connection, or an adhesive connection.
In the drill bits disclosed in U.S. Pat. No. 3,888,320 A, the cutting portion and the drill shaft portion are connected to one another via a removable plug-and-twist connection. The cutting portion comprises an annular portion connected on a first end to a plurality of cutting elements and, on a second end, having an exterior insertion element and an annular limit stop shoulder. The drill shaft portion comprises a cylindrical drill shaft that comprises an interior insertion element having a face on an end facing the cutting portion. The insertion elements form a plug connection in an insertion direction parallel to the axis of rotation. The exterior insertion element comprises a plurality of pin elements in its interior that are directed radially inward in a plane running perpendicular to the axis of rotation. The interior insertion element comprises a plurality of L-shaped clearance slits into which the pin elements are inserted. The L-shaped clearances comprise a transverse slit running perpendicular to the axis of rotation and a connector slit running parallel to the axis of rotation and connecting the transverse slit to a lower edge of the interior insertion element.
In the known drill bit with an exchangeable cutting portion, when the plug-and-twist connection is closed, axial play is present between the cutting portion and the drill shaft portion in a direction parallel to the axis of rotation. A gap is formed between the face of the interior insertion element and the limit stop shoulder of the exterior insertion element such that the transmission of force from the drill shaft portion to the cutting portion occurs exclusively via the pin elements. Moreover, the gap leads to a cooling and rinsing medium not being completely supplied to the work surface, but rather to the possibility of the medium being misdirected into the gap on the interior of the drill bit.
An additional disadvantage of the known drill bit having an exchangeable cutting portion shows itself when the drill bit becomes jammed in the substrate. In core drilling, it is common for the drill bit to become jammed in the substrate during drilling and need to be removed by the operator. In stand-guided core drilling units, in order to remove a jammed drill bit, the drill bit is driven opposite the rotational direction and the drill stand exerts a tensile force on the drill bit directed opposite the drilling direction. The operator attempts to free the drill bit from the substrate by manually turning it with the aid of a tool key and, at the same time, pulling it with the aid of the drill stand. The L-shaped clearances present the risk that the operator will rotate the drill shaft portion around the axis of rotation until the pin element impacts the connector slit and, at the same time, activates the handwheel of the drill stand, such that the pin element is moved out of the connector slit. As soon as the plug-and-twist connection between the cutting portion and the drill shaft portion has been released, the cutting portion must be freed from the substrate using other means, for example, by removing the substrate.
The object of the present invention is to develop a drill bit with an exchangeable cutting portion in which the risk is reduced that, during the removal of a jammed drill bit from the substrate, the plug-and-twist connection of the insertion element is unintentionally opened and the drill shaft portion is removed from the substrate without the cutting portion. Moreover, the stability of the drill bit during drilling and its ability to withstand the exertion of tensile force by a drill stand should be increased.
Provision is made according to the invention for the clearance slits to comprise a connector slit and a transverse slit having a catching region and the locking region, with the catching region being connected to the connector slit on a side of the connector slit facing the direction of rotation and with the locking region being connected to the connector slit on a side of the connector slit opposite the direction of rotation.
The transmission of torque from the drill shaft portion to the cutting portion occurs via the pin elements and the catching region. The locking region is located on the side of the connector slit opposite the catching region. The locking region reduces the risk of the plug-and-twist connection between the drill shaft portion and the cutting portion being unintentionally opened during the removal of a jammed drill bit from the substrate. The operator attempts to free the jammed drill bit from the substrate by rotating the drill shaft portion around the axis of rotation with the aid of a tool key and, at the same time, pulling with the aid of the drill stand. Practical experience has shown that operators primarily pull on the drill shaft portion when the pin element is striking the transverse slits. In the drill bit according to the invention, if the pin element strikes on the catching region or on the locking region, there is no risk that the plug-and-twist connection can be opened. In the drill bit according to the invention, the plug-and-twist connection is only opened if the operator pulls on the drill shaft portion at the precise moment when the pin element is located over the connector slit. The risk of unintentionally opening the plug-and-twist connection is considerably reduced as compared to L-shaped slit clearances.
The height of the connector slit parallel to the axis of rotation is preferably at least 10 mm. A height of at least 10 mm guarantees a sufficient ability of the cutting portion to withstand the tensile force exerted by a drill stand.
Here, it is particularly preferable for the height of the connector slit parallel to the axis of rotation not to exceed 13 mm. Up to a height of 13 mm, the ability of the cutting portion to withstand the tensile force exerted by a drill stand is improved. Greater heights have no influence or very little influence on the ability of the cutting portion to withstand the tensile force exerted by a drill stand and only incur additional material and processing costs.
It is preferable for the transverse slit parallel to the axis of rotation to be located at a lower distance from the annular portion of at least 3 mm. A minimum distance of 3 mm ensures sufficient ability of the cutting portion to withstand the tensile force exerted during the removal of a jammed drill bit with the aid of a drill stand.
Here, it is particularly preferable for the lower distance of the transverse slit from the annular portion not to exceed 5 mm. Up to a distance of 5 mm, the ability of the cutting portion to withstand tensile force is improved. Greater distances have no or very little influence on the ability of the cutting portion to withstand tensile force and only incur additional material and processing costs.
In a preferred embodiment of the drill bit, the pin elements have a pin height perpendicular to the axis of rotation, with the pin height being from 68% to 89% of the shaft width of the drill shaft. The width of the interior insertion element is preferably approximately 50% of the width of the drill shaft. As the pin height increases, the surface area for the transmission of torque increases as well. In addition, ability to withstand tensile force is improved.
It is particularly preferable for the pin elements to be embodied in the shape of a circular cylinder with a pin radius, the pin radius being from 2.5 to 5 mm. The transmission of torque from the drill shaft segment to the cutting segment occurs by way of the pin elements and the outer insertion element. The greater the pin radius of the pin elements, the fewer pin elements are necessary for the transmission of torque.
It is preferable for the width of the catching region to be no less than the pin radius plus 1.5 mm. At this minimum width for the catching region, sufficient ability of the cutting portion to withstand the tensile force exerted by a drill stand is ensured. The pin elements rest against the catching region and do not break out of the catching region.
Here, it is particularly preferable for the width of the catching region to be no greater than the pin radius plus 3 mm. Up to a width of half the pin diameter plus 3 mm, the ability of the cutting portion to withstand the tensile force exerted by a drill stand is improved. Greater widths have no or very little influence on the ability of the cutting portion to withstand tensile force and unnecessarily reduce the stability of the cutting portion.
In a first preferred variant, the width of the catching region and the width of the locking region correspond to one another. Here, the catching region and the locking region have a minimum width of the pin radius plus 1.5 mm. Particularly in the case of drill bits with small diameters, this embodiment allows the portion of the transverse slits on the circumference to be large.
In a second preferred variant, the width of the catching region is greater than the width of the locking region. Here, the catching region and the locking region have a minimum width of the pin radius plus 1.5 mm. This embodiment is particularly advantageous for drill bits with small diameters, in which the proportion of the circumference occupied by transverse slits is large.
In a preferred embodiment, the first insertion element is embodied as an outer insertion element with a limit stop shoulder and the second insertion element is embodied as an inner insertion element having a face. In the connected position, the face of the inner insertion element rests against the limit stop shoulder of the outer insertion element. The transmission of force from the drill bit portion to the cutting portion during drilling occurs by way of the face and the limit stop shoulder. The risk of deformation of the outer insertion element is reduced when the transmission of force does not occur by way of the pin elements, such that the drill bit according to the invention has a high degree of stability. The limit stop shoulder can be embodied in the shape of a ring or a ring segment. By the face resting flat against a ring-shaped limit stop shoulder, the drill bit is embodied in a watertight fashion on the other side, thus preventing the misdirection of a cooling and rinsing medium. The cooling and rinsing medium, for example, supplied via the insertion end of the drill bit, flows in its entirety to the surface being worked and ensures the cooling of the cutting elements and the removal of drillings.
It is particularly preferred for the at least one pin element to be fastened on the outer side of the inner insertion element and the outer insertion element to comprise the at least one slit-shaped clearance. The arrangement of the slit-shaped clearances on the exchangeable cutting portion has the advantage that the less stable of the two drill bits segments is regularly exchanged. The plug-and-twist connection of the insertion elements according to the invention improves the stability of the drill bit as well as its ability to withstand tensile force. The drill bit portion comprising the slit-shaped clearances is more susceptible to deformation by tensile force than the drill bit portion to which the pin elements are attached. The risk of deformation by tensile force increases along with the proportion of the slit-shaped clearances on the circumference of the insertion element. Because the diameter of the outer insertion element is greater than the diameter of the inner insertion element, more circumference is available on the outer insertion element for the slit-shaped clearances, which reduces the proportion taken up by the clearances on the circumference. The drill bit is more stable when the slit-shaped clearances are provided on the outer insertion element.
Due to the arrangement of the pin elements on the inner insertion element and the arrangement of the slit-shaped clearances on the outer insertion element, it is possible for the drill bit to be designed in a watertight fashion on the inside, thus preventing the misdirection of a cooling and rinsing medium. In the case of a watertight drill bit, all of the cooling and rinsing medium supplied, for example, via the insertion end of the drill bit, flows to the drilling surface and ensures the cooling of the cutting elements and the removal of drillings. The drill bit according to the invention also allows the operator to monitor the opening and closing of the plug-and-twist connection. Such monitoring is not possible or is possible only to a limited degree if the slit-shaped clearances are provided on the inner insertion element.
It is particularly preferred for the length of the inner insertion element to be greater than the length of the outer insertion element. The difference in length between the inner and outer insertion elements ensures that the face of the inner insertion element rests against the limit stop shoulder of the outer insertion element and, during drilling, a defined transmission of force occurs from the drill shaft portion to the cutting portion.
It is particularly preferred for the length of the outer insertion element to be at least 18 mm. At a minimum length of 18 mm for the outer insertion element, sufficient resiliency of the cutting portion is ensured. The slit-shaped clearances can be positioned on the outer insertion element at such a height that the cutting portion is fixed against tensile forces that occur during the removal of a jammed drill bit with the aid of a drill stand.
Here, it is particularly preferable for the length of the outer insertion element not to exceed 28 mm. Up to a length of 28 mm for the outer insertion element, the ability of the cutting portion to withstand tensile forces is improved. Greater lengths for the outer insertion element have no or very little influence on the ability of the cutting portion to withstand tensile force and only incur additional material and production costs.
In a preferred embodiment, the outer and inner insertion element are embodied in a ring shape, with the difference between an inner diameter of the outer insertion element and an outer diameter of the inner insertion element being greater than 0.11 mm. The gap thus formed between the outer and inner insertion elements ensures that the face of the inner insertion element rests against the limit stop shoulder of the outer insertion element. The drill bit is designed in a watertight fashion on the inside such that the supply of a liquid or gaseous cooling and rinsing medium to the cutting elements is guaranteed. Moreover, a defined transmission of force occurs from the core drilling unit via the face of the drill shaft segment onto the limit stop shoulder of the cutting portion.
In a preferred embodiment of the drill bit, three or more pin elements are attached to the outside of the inner insertion element and the outer insertion element comprises three or more slit-shaped clearances, with the number of clearances being greater than or equal to the number of pin elements. In the drill bit according to the invention, the transmission of force occurs from the face of the inner insertion element onto the limit stop shoulder of the outer insertion element and the transmission of torque occurs via the pin elements onto the outer insertion element. Here, it is particularly preferred for the pin elements to be evenly distributed around the axis of rotation of the drill bit. The even distribution of the pin elements allows for the assignment of pin elements to clearances to be omitted and a pin element may be inserted into any of the clearances.
The number of the slit-shaped clearances must be greater than or equal to the number of pin elements. In order to close the plug-and-twist connection, a slit-shaped clearance must be provided for each pin element. The design of the drill bit in which the number of clearances is greater than the number of pin elements has the disadvantage that the stability of the cutting portion is unnecessarily reduced. Such a design is only suitable, if at all, for drill bits with very large diameters because, in such drill bits, the proportion of the clearances on the circumference of the outer insertion element is less than is the case in drill bits with small diameters.
It is particularly preferable for six pin elements to be fastened on the outer side of the inner insertion element and for the outer insertion element to comprise six or more slit-shaped clearances. A rotary connection with six pin elements having a pin diameter of 6 mm is suitable for the transmission of torque for drill bits with various diameters, for example, from 50 mm to 250 mm.
In a refinement of the drill bit, the annular portion comprises a guide portion, with the guide portion being flush against an outer edge, an inner edge, or an inner and outer edge of the cutting elements, the edge being parallel to the longitudinal axis. Due to the flush fit of the guide portion with the cutting elements, the guide portion forms a guide for the cutting elements during drilling and stabilizes the cutting elements. Here, guidance may occur on the outside of the drill bit via the substrate surrounding the drill bore or the inside of the drill bit via the drill core.
It is preferable for the length of the guide portion parallel to the axis of rotation to be less than 4 mm. A guide portion that is smaller than 4 mm does not hinder the supply of a cooling and rinsing medium at all, or at least not substantially.
In a preferred embodiment of the drill bit, a nose is disposed on the outside of the inner insertion element and the outer insertion element comprises a groove, with the nose and the groove forming a positive fit in the axial direction in their connected state. Due to the additional positive connection between the drill shaft portion and the cutting portion, the risk of the detachable connection between the drill shaft portion and the cutting portion being unintentionally opened in the course of removing a jammed drill bit from the substrate may be further reduced. The design of the positive attachment means as a nose and a groove allows for a simple and reliable connection that impedes the removal of the drill shaft portion from the cutting portion. The retention forces of the connection may be adapted to the area of operation of the drill bit using the geometry of the nose and the groove.
It is preferable for the nose to be disposed between the pin elements and the drill shaft in the axial direction and for the groove to be disposed in the axial direction at the level of the slit-shaped clearances. Portions develop between the slit-shaped clearances of the outer insertion element that display an elastic effect. The elastic effect can be adjusted via the number and axial height of the slit-shaped clearances and the length of the outer insertion element. In order to separate the drill shaft portion from the cutting portion, a force is exerted in the axial direction on the face of the outer insertion element with the aid of a tool. The exertion of force deflects the elastic segment of the outer insertion element and the positive connection between the nose and the groove can be removed. The greater the distance of the groove from the limit stop shoulder of the outer insertion element, the greater the deflection of the elastic segment.
It is particularly preferred for the groove to have an annular design and be disposed in a plane perpendicular to the axis of rotation. A groove with an annular design that is disposed at the level of the slit-shaped clearances supports the elastic effect of the portions of the outer insertion element between the slit-shaped clearances.
The axial direction is defined here as a direction parallel to the axis of rotation of the drill bit. In the connected state of the drill bit portions, the axis of rotation of the drill bit coincides with the longitudinal axes of the drill bit portions, the cutting portion, and the drill shaft portion. A radial plane is defined as a plane perpendicular to the axis of rotation, and a radial direction is a direction running in the radial plane and intersecting the rotational axes of the drill bit or the longitudinal axis of the drill bit portions.
Exemplary embodiments of the invention will be described below with reference to the drawings. The drawings are not necessarily intended to show the exemplary embodiments to scale; rather, the drawings are shown in a schematic and/or slightly distorted manner when it aids understanding to do so. With regard to elaborations on the teachings immediately discernible from the drawings, we refer to the relevant prior art. It should be noted here that numerous modifications and alterations may be made regarding the form and details of an embodiment without deviating from the general concept of the invention. The features of the invention disclosed in the specification, the drawings, and the claims may be considered essential to the refinement of the invention either alone or in any combination. In addition, all combinations of at least two features disclosed in the specification, the drawings, and/or the claims may be considered to fall within the scope of the invention. The general concept of the invention is not limited to the exact form or details of the exemplary embodiment shown and described in the following or limited to an object that would be considered limited in comparison to the object disclosed in the claims. In the case of measurement ranges given, values lying within the ranges named as boundary values should also be considered claimed and usable in any desired manner. For the sake of simplicity, the same reference characters have been used in the following for identical or similar parts or parts with an identical or similar function.